Thin film metal alloy disks for vertical magnetic recording typically comprise a substrate, a nonmagnetic underlayer formed on the substrate and a magnetic layer having an ordered crystalline formation with a generally perpendicular magnetic anisotropy formed on the nonmagnetic underlayer. One type of material used as the magnetic layer is a cobalt-chromium (CoCr) alloy which is sputter-deposited to form a film having a hexagonal close packed (HCP) crystalline structure with the [00.2] axis (the C-axis) oriented perpendicular to the disk substrate. An important factor in the production of vertical magnetic recording media is the ability to control the orientation of the HCP CoCr or cobalt-chromium-X (CoCrX) alloy magnetic layer. The degree to which the C-axis of the HCP structure can be aligned perpendicular to the substrate strongly influences the magnetic properties, such as the perpendicular and horizontal coercivities.
The magnetic properties of a thin film alloy disk made with various substrates, a titanium (Ti) underlayer and a CoCr perpendicular magnetic layer are described by Kobayashi, et al. in "High Density Perpendicular Magnetic Recording on Rigid Disks", Fujitsu Scientific and Technical Journal, Vol. 19, No. 1, pp. 99-126, March, 1983. That article discloses that substantially improved perpendicular magnetic anisotropy of the CoCr film is achieved with the use of a Ti underlayer, and suggests that the C-axis orientation of the CoCr film is improved because the Ti underlayer isolates the influence of the substrate from the CoCr film. A thin film alloy disk having a nonmagnetic cobalt-tantalum (CoTa) alloy as an underlayer for a CoCr perpendicular magnetic layer is disclosed in Japanese published unexamined patent application No. 59-77620 assigned to Suwa Seikosha Co., Ltd.
It is also known to use ternary alloys, such as cobalt-chromium-tantalum (CoCrTa), as the material for the magnetic layer. Published European patent application no. 93838 assigned to Teijin, Ltd. discloses a disk for vertical magnetic recording having a soft magnetic underlayer of an amorphous CoTa alloy and a magnetic layer of CoCrTa with perpendicular magnetic anisotropy. The magnetic properties of a vertical recording disk with an 8000 Angstroms thick CoCrTa magnetic layer deposited on a 1000 Angstroms thick Cr underlayer are described by Langland and Albert in "Recording on Perpendicular Anisotropy Media with Ring Heads", IEEE Transactions on Magnetics, Vol. MAG17, No. 6, November, 1981, pp. 2547-2549.